Warfare is employed to bring about or to resist political, social, or economic changes. History provides evidence of such tangible, and frequently interrelated, causes as religious conflict, protection of dynastic succession, or acquisition of territory. War for acquisition of land is directly related to the necessity of providing food for a nation or a group. Wars are also often linked to a desire for security, on the theory that a so-called first strike prevents an enemy from carrying out threats. According to some much disputed theories, such as those of the Austrian zoologist Konrad Lorenz, innate aggressive drives are responsible for human beings' frequent recourse to warfare.